A door, crushed under a rockfall. If they buried it, they mean to abandon it.

[ Finished, in other words. Not an active site. Truthfully, Geralt can't confirm the tampering, either. It was Sam who spotted that discrepancy, and Geralt trusts Sam enough to take the man at his word. ]

There's more. When we entered the cavern, it released a toxin into the air. Nearly took out one of us. In any case, breaking down that door isn't worth what it might unleash.

[ This is how entire villages become cursed with the plague. He nods at the lizard in the tank. ]

You might have better luck following that creature's trail. Something tells me the source of it is not as foreign as it appears.